Quotes from The Joker: Part 1

The Joker: Don't talk like one of them. You're not! Even if you'd like to be. To them, you're just a freak, like me! They need you right now, but when they don't, they'll cast you out, like a leper! You see, their morals, their code, it's a bad joke. Dropped at the first sign of trouble. They're only as good as the world allows them to be. I'll show you. When the chips are down, these... these civilized people, they'll eat each other. See, I'm not a monster. I'm just ahead of the curve.

Honesty. People in all reality do what they want to, only afterwards attributing (inventing) the logic behind their actions to heroic, moral, or chaotic causes. Creative rationalization is the foundation of society. The truth (& general agreement) of the lie.